It is known to provide an EOAT to grip objects for robots. The common EOAT gripper has a linkage which is pivotally connected to a hydraulic or pneumatic actuator. Prior to the present invention, a change in the gripping force exerted by the gripper required a change in the force exerted by the actuator. The above mandates that the pneumatic or hydraulic system used for powering the actuator have a variable pressure system, therefore requiring a pressure regulator to give the desired actuator pressure. It is desirable to provide an EOAT gripper whose gripping force may be modified without changing the actuator force.
Another characteristic of EOAT grippers before the present invention is that most grippers are ideally suited to handle workpieces with regular polygonal cross sectional areas within a rather limited dimensional range. When changing dimensional sizes or changing workpiece shape, it is usually required to design another EOAT gripper. Therefore, the robot must be supplied with the separate EOAT gripper whenever the workpiece is dimensionally changed. It is desirable to provide an EOAT gripper which can easily be adjusted to handle workpieces in a wider dimensional range. It is also desirable to provide an EOAT gripper which can be used on workpieces having various cross sectional shapes, many of which do not have a regular polygonal cross sectional area.